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Michelle's slit mask currently contains five slits for spectroscopy as well as an "open" mask for imaging. Resolving power is inversely proportional to slit width. The width of the two-pixel wide slit (~0.4") somewhat exceeds the diffraction limit in the 10um window (1.2 lambda/D at Gemini corresponds to 0.3" at 10.0um), and is narrower than the diffraction limit in the 20um window. The three-pixel wide slit is a better match at 20um. Our best estimate of the imaging pixel scale is 0.1005 arc-seconds per pixel, based upon binary star separation measurements.

A list of the Michelle broad and narrow-band filters is presented here. Since the filter wheel is common to both the imaging and the spectroscopic light paths the filters are available in both modes. The longpass filters are used for lowN and MedN1 spectroscopy, while the narrow-band filters are used with the higher-resolution modes (all spectroscopy filter selection is done internally by Michelle and need not be specified by the PI). Transmission data are available for some filters, as indicated.

Basic characteristics of Michelle's spectroscopy modes

Michelle uses an entrance window made of Potassium Bromide (KBr). KBr has a transmission of ~90% across the mid-infrared. Since KBr is hygroscopic, all contact between water with the window must be minimized. This includes dew that may form on the window while observing under high humidity conditions. The humidity limit for observing with Michelle at Gemini is a relative humidity of 80%. During its use at UKIRT, a protective "sacrificial window" system was implemented to help prevent damage to the cryostat window that serves as the vacuum seal between the dewar and the atmosphere.

The properties of NIRI in imaging mode are summarized in the following sections. Three selectable fields of view and pixel scales are available. With adaptive optics NIRI is available at f/32 for J-L' imaging (but see caveats for L'), and at f/14 for imaging out to 2.5 microns due to the increased thermal background. Imaging at L' is impossible at f/6 and only sometimes possible at f/14. The narrow band L filters (e.g., the PAH filter, Br alpha) can be observed at f/32, f/14, and f/6. M' imaging is only possible at f/32.

How to observe with Gemini. Is this better as an expanded menu with a lot of items, as it is now (broken up by headings for Phase I and Phase II), or with just 3 expandable subheadings beneath it, or broken into two categories (phases 1 and 2) at the top level?